Magnet casting



Aug. 3, 1943. M. P; lczHRlsTENsEN MAGNET CASTING FiledMay 26, 194.1 3 Sheets-Sheet 1 Aug. J3, 11943. M. P. :cHRlsTaENsEN' MAGNET CASTING Filled vMay 26, 1941 Aug 3, 1943- M. P. cHRfsTENsl-:N 2,325,832

MAGNET CASTING Filed May 26, 1941 l 3 sheets-Sheet 3 Patented Aug. 3, 1943 UNITEDSTATES PAT ENT; OFFICE' n v'iillAdnntr CASTING e e Y Y Mitchell PQ Christensen, Chicago, Ill., assigner to' .l j Belden Manufacturing Companyg-a c orporationg- Y Application May '26," 194i', serial Np.- 395.243

' 12 claims: (o1. 2li-155.5)

flvIy invention relates generally to thejpr'ovil son of inexpensive, small, permanent magnets .Y

for use in connjection withV dynamic soundv producing mechanisms, such as radio loud Aspealiers and the like.

In recent years magneticjY metals 'of improved alloy {,:Vom'positionsY havebeen developed ont'Vv of which permanent magnets having muchfgreater magnetic Vstrength than'previously obtainable may be formed.V These improved magnetic metals generally comprise various nickel-#aluminum alf. v

lcys einen. A very important application o fthese improved'permanent magnets ofV greater magnetic strength has been in `connection with loud speakers for radios,` record players, andthe,

like. Because of the r'equirements'in respectfto minimum space and weight, ordinary iron orQst'eel permanent magnets do not have sufficient inagnetic strength per unit' density vto permit themltoY Y be usedto provide thek magnetic' field in tlleseV loud speaker devices, Vand it wastheV practice prior tothe development oi the Yimproved Y* magnetic Valloys to, use elec'tromagnets'forv providing the` 'magnetic field in connection these loud speakers. However; `these improved magnetic' alloys provide permanent magnets having rsuincient magnetic strength per unit density to permit them to replace the electromagnets, especialf end Y'ofthe bolt or'v screw engages the 'small cylindrical pole pieceon the narrow pole face'ofv. the

magnetandthe opposite endengages the stirrup Y or like-shaped pole piece or member. Bytightening the Aboltor screw, fthe'small :pole jpiece" is drawnnto contact. with the jnarrow'pole facev magnetis held ingplace-in thejstirru'p. `j

ofthe permanent magnet while the permanent Becausef of thebrttleness and diiiicultly ma.,-Y chineabie Acharacterfof `'the permanent magnet alloys',l vthe provisidnofthese centralvzhbls' rman. economical'gjmannerj y,has yfjgiven fconsiderable ly' in Vconnection with the Smaller size of vloud.

demandare veryimport'ant'factors. Y A V Thefmounting of thesmall permanentmagnets inthe loud speakers Vhas presented somewhat o a problem to the manufacturers o-,these speakers where low costpand low electrical power devices. In order toI provide the greatest magnetic eld strength with minimum iluxleakage,

Vit is desirableto make the' magnets in'thev'formV 'of small Ytapered blockswhereby'one pole is narrower' than thelother. YIn one ofthebest knewn yaifrangement's asmall -cylindrical pole Yp'iece'o'f high permeability i's`mounted on the narrow 'pole 4face of the' tapered magnet and themagnet is Y mountedV in a lstirrrup. or "similarly shaped V'fpo'le piece member which extends fror'nfthev b aseor i' 'large poleface of theepe'rm'anent magnet around the sides'thereof and into close proximity with the smallpole piecev s'o'as to'providea magnetic eld therebetvveen. A

' lunas been i undthat the mest practical way, Y

or at.y least themost convenient way,` of mountingV the` tapered magnets inpermanent 'magnet structures of this type', is to bolt ythe magnetin place by the useof abolt'rorscrewvwhich,passes ythrough a centralhole or passageway extending 'iromf pole Yto pole through each" magnet.V` 'One magnets may be. convenien'tlyV provided rifnfthe desired shape giving maximumfeld strength with minimumv flux leakage without sacrice vor comtrouble/rn fact,it,.hasjb eengfqund."menthej e metal is jeslo hard" and brittle that -itis impractical to drillftheholes by 'ordinary'r manufacturing j nie'th'ods.'Y'Y Accordingliit hasfbeer'i necessary in casting these small tapered magnets v*to use small 1 corestoprovide thecentraliholes therethrough.

This practice has inaterfiallylt increased the oost oicproducingv these ysmall" .;I nagfn'et's 'and various.' .attempts'have been made toeliminatethis expenf sive item of manufacture. lnone caseattempts 'were'i'nadeto' cement the small'pele pieces onto the narrow poles'of the'taperedmagnets. andfto Y Acementfthe magnets tothe 'stirr'psforlike mem-` bersjitlis was,v not a A,satisiao'toryarrangement.

AsanetherV alternative,` small specially` shaped' Y v individual -casting'sof magnetic metal were made iny such shapesY thatcores were notplnecessary.v

However, the'costof making such indivdnallcastings washig'hiand'th'e castingjsvdid not havethe optimum shape for maximum ecienc'y in` respect to greatest magnetic*field strengthwith A minimumA u'x leakage.V ','Otlfler procedures 1have 7 35'` likewise'y prevent"unsatisfactory; and as a' result' therefhasbeen a substantial needV and demand .7. for jprovidn'g.'` small. 'magnets` Vinthaform of Y tapered.loloclishavinglholes.rmelthertljlrongh i e in'a'iesstclstly mannerithanknqwnhertcfofe.

'The object of my invention', generallyv stated, is.v

rto provide vsmall;magnets or" tlietvpe described above: having central holes' passirigtherethrogh by a method vinvolving certain novel-shaped fbar castings, wherehyvthelc'entral.holes are formed withoutthe necessity vof* drilllng'for oi 'u'sifngsmall cores in casting. The 'invention makesp'ossible they manufacture of these .small `magnets'Y on'faf `quantity productionscale ataverylcw cost, The

promise jin respect; toV magnetic eldefligciencyf size, 'mounting arrangement or any Aother' factor. O ther 'obj ects of the vi'rn'lein'sion willfin parti be obviousand in partfstated hereinafter'. f

For `Aa more K- complete understanding of the nature and scope of my invention, reference may be had to the following detailed description thereof taken in conjunction with the accompanying drawings, in which:

Fig. 1 is a perspective-view of a `bar-shaped casting of magnetic metal adapted to be broken up into uniformly shaped pieces combinable to form smallmagnets having central holes passi-ng therethrough, the shape of the casting constituting an important feature of this invention;

Fig. 2 is a vertical sectional view taken on line i' 2 2 of Fig. 1;

Fig. 3 is aV fragmentary side elevational View'of y a machine Vby which the bar-shaped casting-.off- Fig. 1 may be conveniently chopped or broken into short lengths; Y

Fig. `l is a perspective View ofone of .theshort lengths of the bar of Fig. l as chopped ol in thel machine of Fig. 3;

Fig. -is a diagrammatic View illustrating the .nanna in whioathe shoirt'lengfh of ,Fia amai ble.brokenfin twovbya hammer at the thin sec# Y menthe-reef;

" .ig'.` 6 lsapersp'ectiveview oi one of thenniformly shaped pieces obtained by ,breaking shortV permanent magnetjstructu'r'e oa ,loud speaker.; "fjFig, 9 is a sectional view taken Online .S3-#Q of i" l0, is a perspective View ofa'n' alternative j`.Fig l1l is a'vertical'sectional View 'tak I O i` Fig. 10;` .j

`Fig1112 is a perspective'viewofa'short length tiiitopuhioh thebareshaped casting of'Fig. l1Q is aaltedto'bebmken" Figo 13. on@ 14. are oersoootvorvievS-of ii ',C'omplernentary piecesjjnto which the short length 'Gf-Fie.` 12 may bej 'broken at the thin section Fig. 15 isa perspective view'showing the man.-

ner in 'which the pieces of vFigs 13 andlfl may be "f combined to form av twofpiece magnet having a l hole passing therethrough.

` In Fia. 'lofthodrowiea reotongolot bar casting I 0 'isshown which may be readily cast'jn an easy mannerwthout the use of cores'. The barfljhas'a deep longitudinal channel I lffornied inthe top facej! thereof of suchdepth as toleave 'j only aj relatively 'thin "section "i3 'interconnect-ing f theportions "of the bar'fon opposite sidesf'of the "channel, V'It Will be noted that'the'sides "of the channel I! slope orjtaper inwardlyjat a substaflv. ktial angle. A number of regularly spacedver'- toai, grooves. I4 .are formed, inthe' Opposite SdeS f 'offthebar l il, asshown. The groovesld are semicylindrical in shape, but it'will be understoodthat they maytake other forms ii desired. Afterthe bar lhas` been cast, the top and bottom faces 12j andV lI Sarei smoothed'and plained bygrir'idin'g-Y s o f that the thickness ofthe bar `s o between tnefajces `Wil1 beuniform throughout. The

.bastin any practical length. When thebar lil Vis cast or formed .of .aperjmanent magneticlmetal, suchas, the nickel-'alu- *minurn alloys of "iron,jit willfbe otsuchhardf 'T c'fombied together to vforin aj `small tapered'magl 'n'etf having a centralhole formedf'therethrough;

' j' `iliig. jf 5fis ja sidev elevational'vieWQpartly broken e awaif'fshowmg the 'manner in'which the twegpiece magnetjof Fig. "1 maybejjasse'inbled as partei the .-and'chv The Shorighroko ,jill fhohao fittasi showln- It' 'will that certain ott` e11 ness and brittleness that it can be machined only with great diiiioulty, although it may be ground fairly readily. However, this brittleness or hardness permits the bar I0 to be readily chopped or broken into short lengths of predetermined size. Such a short length is shown at i6 in Fig. 4, and

in Fig. 3 of the drawings a machine for forming these short lengths is shown.

.'Ifhelmacl'iiejis indicatedfgenerallyat E? in Fig; 3,- and comprises lbed'"rri'ember'il which servesl as a supportingbase for the elements thereof. A block 2i is mounted on the base 2E! .andifour upright posts -22 are supported thereon,

as shown. VA guide block 23 is supported by the fourposts 22 adjacent'to the upper ends thereof,

andl-s`erveslto guide the Vertical up and down reciprocating movement of a post 24 carrying a block 2 5 on the lower Vend thereof.

'I'he'lrarsY VIt) are'chopped into short lengths I6 by-a pairof oppositely disposed knife-edged mem- Vbers'or blocks 26and 21. 'lhelower knife-.edge member 25. is securely mounted en the block 2l, while thf uppe'r .knife-eds? member ,'21. isse eureiy; heidi on" the [lower 'of "the pearl. 2 4..

' vTlfelovver'knife-'edgel member v2'6`is. stationary while. .the upper member 2 7, is moved uli and 'fdownf when f the` machine; Vi.' is in "operation by 'suitablefpowerf and controll mean'sfconneoted with 4thepost lfLv e f The bars Vljaref adapted'to lie'iedinto .the mai chine .l1 on .narrowigjuide tabiejso having] a "dhof'thabar's lil.,Y The floorof thechannel injtheftable' islevel vwith'j the heiehtof the. knifefiedee. 311- orthe' lower. "block 2 6 .sof that thegbottomiface of. vtho borfjl will Test hr'okeniine 32. 1 Injorider' thaty the bar Imay. .bek

' Y .tipush'issumoionttoad# vahootllo bo Costing;.IOgfromone'setof opposite L4; .to .thoothoa 'Eaohtime. .the 4""hfol lower. 'Cutting'. block clj 2 1 jwill vcome down .f ,thez-tpp or themen lo pjor br ak f1 a short length I6 thereof.

12.6, the; .speer "Qottin with, Sharp. lilo. y acto.

V0.11 as. may' b-eproviood to. oriopf op 'the bar.-

" Sii'oo the. short. .lengths il 6I. have. -only :a .thin

sootiooql. .oonnootinsifthe .tivo halves thereof,

lengthsdlis insertedbetweenftlief j afWS" ofa Vice e .feeomgitaue an, as

. after.

whichY is indicated at 42, willv easilybreak-the piece I6 in two. VThe brokenpieces are indicated at 431D Fig. 6. 1

ytion of one o f the opposite `vertical sides-ofthe bar YHl. Therfaoe 45 and the groove .I4 yare perpendicular to the `parallel aces-44 and 45.

The face 41 opposite togthe vertical ,facef451is sloping yand originally was part ofk onejofathe slopingsides of ythe channel il of; the bar I0. Q Each'pair of the pieces 43may be combined together so as to form a two-piece taperedmagnetvrhavinga central hole I passing .therethrough asshown in Fig. '1. The narrow pole faces 44 ofthe pieces 43 are .placed together 'l side by side in plane alignment sothat they twopiece magnet 5B is tapered from its base tothe top. Each of the piecesr43 is-mragnetized sorthat the narrow faces 44. form pole Y faces of like polarity while theopposite faces45 formtheopposite pole faces of opposite polarity. Since the Y pieces 4 3 are placed together with likepolesadf Y. jacent to. eachother, itV lwill bef seenthatlthe l.

pieces tend to repel each other-and to separate fand spread apart. However; when assembledjin obtainedwith `afminimum-sized magnet and With fa.minimum-,oflinx-leakage, A 51.5.@ Y

Y My. invention mayfbepracticed andembodied in-,severalldiier'ent modifications. 'Referring to 1 j Figs.;10f.andiv11of thefdrawings. an alternative 1 Y ormgro'f barshapedrcasting.10'fofmagnetic metalV the magnet structure of a loud speaker, the

pieces ,43 are held togetheras will appear herein# In Figs. Sand ala-permanent magnet structure fora radioloud speaker is indicatedgenerallyy at lwhich has for the energizing element-thereoiatwo-piece permanent magnet 56 Lwhich corresponds to the two piece magnet 5D of- Fig.w'1. A cylindrical pole piece 51 of high permeability isfsupported on the narrow pole face of the magnet 56 by a supporting flanger58, asfshown.v The opposite wide pole face of the magnet 56 ts against one side 60 ofla stirrup-shaped pole piece 6i. `The cylindrical pole pieceY 51 and* the permanent magnet 56 are held-in assembled. relationship in the stirrup-shaped polegpieceY 6l by a bolt 62 which passes through the central hole in the two piece magnet 56;- The head k63 of the f bolt 62 engages the backrof the side ,65 `*ofthe stirrup 6i while the inner threadedend thereof isV screwed into the-cylindrical polepicce;` 51l which is tapped to receive the same. It will be seen thatrby drawing down zorgtightening the bolt 62i the pole, piece 51 is' drawn down against Dartsof the bar 10. .Regularlyg'spaced;*vertical side grooves V14/ are .formed vin-'one "of the sides equivalent to a similarly;shaped'magnet which is fcompletelyj integral: throughout. :'As Vfarlfas the'. operation, assembly? and'v ruggedness of the',V

speaker 'is' concerned',r the Atwo'fpiecegmagnet-v 56 is equally assatisfactory asv anA integral fone. Howeverfas pointed out above, the hole'therethrough or accommodating fthe assembly retaining. screw 62 is `formed without difliculty and without the necessity of drilling or using cores in casting.

Thus; the'cost offthemagnetsLSG isma'terially -1- It was indicatedyaba/einconnection` with the .description oftheba'r-shapedcastingl of Figs.

1 and ,2,lthat1the`rewasfan.advantage inhaving the.l long;I longitudinal"Y .channel :l therethrough formedy with;l tapering orzinwardlyf sloping vsides'.` In v the'V lrstzplace; .thisetaper 'permit'sl the. =mold pattern :ot the castinggto .be easlyremoved .from v the mold; and in the Second place', it provides the .two-pieceilmagnetfwith aY taper which is very desirable. s. Thisfftaper Yallows n,the fluxzfof 'the magnet 56}:'to,;be concentrated at d. a narrow pole space whereby-'a1 maximum! ofthe magneticfflu'x will f linkl across theV annular` airfga'p 65..v V@In this manner :the maximum l strength 'of eld 'fluxv is is.` shownywhich is`E adapted -to be brokenu'p Ato form. into.' pieces-which-jmaybe lcombined in pairs toformpermanent,magnets eachhaving aghole Y passingl therethrough. V a-The.` bar 'casting 10 has two longitudinal v:channels 1I and 1.2 formedin the toplfand bottomsurfaces thereof." and., placed oi center toward-oneside.l Thechannels" 1I and f 12l are'Y vertically `opposite-so as pto'v leave" only f a small inarrow `section .13.lco-nnectingithe -two ofwth'e bar 10, asr shown. Thev vgrooves. 14 are yofsubstantial*size;sov as toi-adequately 'accom'fl Y modate a bolt or screw, such as .fthe bolt v612' of f finie-.nario maybe chppeaintosnrtiefigtiis v 5 as* show.nin'fFig.Y l2 according tothe manner" .describedV in connection with `-the breaking? vof the bars leinthe machine I1, Fig.V 3 of`y the v drayvings; -Each of the Vshort lengths 15 contains of the shortiengthsgs' may be broken igtw'o the two-part narrow pole'facego'f the magnet '56 and the magnet 56 is Ain turn heldrmly against the inside of the stirrup'6l. vThe boltvz'draws the pole piece 51 in sufficiently tightly so 1 asjto heldthe two pieces, of; the magnet 56 `together and overcome the repulsion therebetween. p The stirrup 6| extends around the sidesof the magnet 55 and hasA a hole formed in,the side E4,I opposite'the side 6), which fits around the pole piece `51 so asV to form an annular: air gap E5 therebetween.` The lvoice coil (notshown) of the. speaker will t inthisv air gap v6,5; A metal basketor spiderv 66 of the usualconstruction is provided on thefleftphand side Yof the stirrup El as shown in Fig. 8 and'is adapted to loeV conveniently spot-welded top -the stirrupgl, or otherwise suitably secured,l theretoen oneQOf the. deep side Vgroovesrvf14..jInturn, each atl the thin section .13.thereof/solfasto form thel v4complementary rpieces,- 16. and2 11 shown in Figs.13and v1'4. respectively. Each complemenitar-y set or pairoffpieces 16 and 11may becomlto d support the usual vibrating or sound Vproducing coneof the speaker. Themetal basket 66may -binedtogether as lshowninV Fig. l5 so as to form a -magnet r 18,. having aj central hole 219 passing therethrough: vvThe hole 19 is formed by Yone of the .vertical-.side grooves-14v and closedv by thefabutting sideJof the pecefl. The `magnetv 16J mayr be assembled in "a permanent'magnet structure inlthe` manner inlwhich the magnet S6-is assembledin thepermanentmagnei; str'u'cf f Ature-55,'lign8..gY :ff' 'l IIL-the foregoing descriptio'nvofV certain embodiy f ments of my inventionand in the appended claims various pieces and-elements have beenlsh'own or describedY by reference tofcertain positions. That is,V the top and :bottom faces; vertical sides, and d other portions :of "the pieces have been referred to.,V `ItV willxbe understood thatv suchfpos'itions maybe changedfreversed;v and altered and thatl 'Y The two-piece. '-.ma'gnet 56; is functionally referencei-:to certain positions has'lbeeniforspurpzvse'siof'description:only:'awr:L

bo'diments yof the vdriventionmi'aly: be lmadewithout departing from Y thef/seope "thereof, itetsllntended that allmatterdeseribed hereinbetorefpr shownv'lineathe acoompanyingsdrawingsg'gshallebe castingpng:opposite-sides of.f'saidchannel,ffand Y having/. plurality offfgrooves extendlngfbetween Y ofthe casting. .if Y; ai A castingrof 'diff'cultlymachinable-permae nent Imagnet metal shapedins theform Yofflafreci tangularba-r having -a deeplongitudinal channel in 'either thetop,Y or.: bottom faceithereoffofvsuch depth 'as to Ar leave `only 'afrelativelythinfrrsection connecting?IA the portions of f the 1barshpedi`^cast ingon roppositesides; of said' channel, i and'fhavl ing a plurality of regularly `spaced 'aver-tical grooves in the opposite'sidesthereofs:'1i 1f= r 1 r 3; A :casting: of fdifcultly machinable lperrnaL ne'nt1magnetmetal shapedinthe lfor-xm of-larectangula'r barlhavin'g az'deepi-longitudinal channel in Vthe center :of eitherlthe=top -oeflbottomfvface thereof of suchdepth aasztoleaveonly La VIrelatively thin section 1connectingtheitwofvlhalves `ofl'the bar-shaped castingfonfopposite sidesi-of said i channel, "and ''havingfa 'plurality iofi'regw larlyspaced'vertioal-grooves in` theopposite-'sides thereof with. ,theefgroov'es onf one 'side being5 di- Q rectlyopposite to those'on the' other' side.

@4. Af casting of difcultly :maohinable permanent magnet metalshaped in theform ofralree tangular -bar having a-deep longitudinal-channel the topfrface thereof '-'With inwardly sloping sideszandf ofieuohV depths/faste* leave? only gemela# tively thin =seotion lengthwise 'of-fthe :fbar icon# meeting the portions of the bar on oppositesides Y of `,said chlanneLfandy having-za *plurality firgularly` spaced v vertical."A grooves :extending fbetwe'en the top and bottomfacesfin 'atleastoneqside'of thecasting. c

nent magnetmetalshaped infthefo'rmfof a'1 rec# itanfgfular,l oarv having :a deep longitudinal-:channel :intlietop face thereof-'with inwardly and of L such depthaasY tofaleaveonlyv a L relatively' thin- .section lengthwise-t; the.barconnectinglthe portions of the bar fion -opjpositeisides of'` sal'fl oharinel,A and hav-lng v9a'L plurality hof: regularly spaced vertical grooves inffthe:loppositepsides thereof with the 'grooves :one one 'sidegbengxii-i reotlyeopposite tothoseon theeotheriside@l l" l kii-6., A-castingof brittle permanentmagnetfmetal' mee reof fofsuh depthJ as -Ctofieave `orilyf-a relatively thiimsection vlengthwise `connectingfthe portions of the bar on' opposite sides. of said channel'rand lllxaving` i a 'plurality of grooves -extending'lbetween 'the '.top nand loottom faces 'in r at leastzonefs'idemf the.bar,fchopping said bar into rlativelyfishort lengths breaking eachY of said shoitiengthsin two fatffthethin '-se'ction` thereof soeistofnrnra pluralityof eomplementarypieces, anxlcombinirrgv theapi'eces 'ft'o'getheri to I form 1` multi# piennagnetsreachofrwhioh has? one of lsaid side groovesfsforming :az-'hole etherethrough. :1558. Ther method f of' .making `magnets each yhaving alhole i therethrough'lwhich comprises, -'casting rdcultly imachinable Vlpermanent .-:magnet metaliin-lthe f orm: Yof 'a 1 'bar having .fade'ep:longi tudinalrchannellin' either! the top or l bottom' face thereof. of such'de'pth as to leave onlyiarelatively thin fsectionl-connectin'g the portions of the Y bar oniopposltefsides of 7said" `channel, and having "a plurality21:51"Y regularly spaced vertical "grooves in the-opposite f'side's thereof,l :chopping said Ibar into a1 number? of frelativelyshortflengthseach ofl f Eincludes `A`al :paiiv of r opposite -vertioa'l grooves, 'rea1kng reach" ofsaid 'short lengths` :in

Y two at' the=thin'section-thereoffeo as -to form a pluralityiof'complementarya ieces eachpf which has oneof sa'i'il'vrtioal-groovesinfohe faeelthereofi and :"'combining' thefcorfipeinentary pieces in pan s toi forni- `twofpiecelm'agn'ets With-1 the Yvertie' .form v--a-fhc" le through each of ythe twoepieoe 519. @Themethod 'of making magnets each l having a central hole therethrough Whioho-mprises, 'castingdiiili'oultly machinable permanent magnet metalfintoltheifor-m of a-barhavinaa deep longi# tudinall -leh-annel Viri-the--Center 'o-f'- 'either the top 'orl-hottoiznffaeethe'reof` of such` depthvasto leave only 1a relatively thfn section'.v connecting* they ltwo halvesl of'the lherr-'voiroppositeasidesl of; saiflch'an-` nel,'-an'd` having' la; plurality 'of regularly -spaced verticallgrooves n'fth'e oppositesi'des-thereof with thegrooVeseon-foneside being dijiectlyroppo'steftothose fon;y thefotheside, choppingfxsa'id barv at rightffan feV to `its-f-llerigth"intorelatively short- 'lengths li ffwvhieheineluries one "setof said opposite verticalf 'side grooves; breaking each rof fs'aitl short '-flength's 'Zin l'tv/o fat the -thin section thereoffAsof-fasi to-iform plurality` of uniformly A"shaped complementary pieces-y eaeh o-f'which `has one-'off the V.-vertieal #grooves inone i face thereof?,

' andlfoonibining the complementary 'pieces inpairs so Iastofornzvtwo-piece `:maier-iets with theY vertical -igroov'esfof reach vpair' ofA pieces placed'l `together =so 'las tofform a icent'ralhole through each of thetwofpiecerniagnets;' i

0 '.ifIl'helfmetl-iodV of-fmakinff tapered-imagnets eac-rtl havihg-=l a Ehole therethrough which:J com-l vprises,'casting-=tlifioultlylanaehinahle f permanent magnet: metalPi the I forni' ofa" 'rectangular bar havinal'axieep lorigitudinal Yfch'annelin e the top fz-roel thereof fflith'- inWardlylfslopineesidesY and of -shaped-inftheform of aareotangular barfhalvirg a .pa-ir? of vertically: oppositel deep ol'ianne'l'srer:-

' tending: longitudinally :ini the; top andai-bottoni "faces thereof of such depth as tosfleaivef'only'a relatlively` thin section tl-ierebetweeniandhaving :a Y vpluralityv Yof f regula-rlyffspacedf vertical? Vgrooves `in.oneside-thereof.' .t 7. The i method. of making :magnetsfeach avV ingY a-hole therethrough Wrhiohf.:compnisescasti I Y anni:

'tica grooves -in the vopposite sidesthereof; chop- Subh depth as tol -leaveenly a` relatively thinseo- -tion E`lengthvv-ise' off'the bar `connecting the-por -tonslof thebar-'hnoppositesides of sadchannel,

' Wing y'a pluralityV of i regularlyv space'drverplage-Said' hareatright angflesito itsv length -ihto relativelyshortlengthsylbreaking".each of said 'slfiort'- lengths inf-twoatthe thin`l` seetion thereof complementary pieces eaeh ofi-Which hasA one yface -vlfliiclr'-oonstitute'd afporti'on fof sai'df-top face of the bar andkan opposite 'paralllzwider fffaee frgrooves-'ofi'reachpair of pieees-cornloiriedto A 2,325,332A f y q -5 which constituted aportion of the bottom `face p of said bar, Veach of said pieces having another' face which is perpendicular to said opposite par'- allel faces thereof and whichconstituted a por-v tion of one of the vertical sides ci said bar-and includes one of said vertical side grooves therein,

and another face of` each Ypiece being opposite. Y to said perpendicular face thereof and which f constituted a portion er one vof said sloping Vchannel sides; and combining the complementary pieces in pairs so as to form tapered twopiece magnets with the vertical grooves of each center thereof, and another face of Veachpiece being opposite to said' perpendicular-.face thereof andwhich constituted a portion ci one of'said f sloping channel sides; and combining the complementary pieces in pairs so as'to form tap-ered two-piece Inagnetswith the vertical grooves of each pair of'piecesr placed together so as to form pair of pieces placed together so'as to form al hole through each of the tapered;- two-piece magnets.

11. The method of making tapered magnets` each having a central hole therethrough which' comprises; casting difcultly machinable permanent magnet metal in the form of a rectangularv bar having a deep longitudinal channel withV inwardly sloping sides in the top" face thereof of such depth as to leave'only arelatively thin secl' tionl lengthwise of the bar connecting the'portions of the bar on opposite sides of said channel,

and having a` pluralityy of regularly. spaced ver-` tical grooves vin the opposite sides thereof with thek grooves on one side 'being directly opposite to those on the other side; chopping said bar at right angles to its length midway between each set of opposite vertical grooves into a number of` relatively short lengthspbreaking each of said short lengths in'two at the thin section thereof so as to form a plurality ofuniformly shaped l two at the thin section thereof so las to form tvvol Y' pieces of the other group so as toform two-piece Y complementary pieces each of which has one Y face which constituted a portion of said top face of the bar and an opposite parallel Widerface which constituted a portion of the bottom face a centralholev through each tapered two-piece vmagnet l12.` The method of making magnets each having aY central hole therethrough which cornprisesg'-` Y casting difficultly machinable permanent magnet metal in the forni of a rectangular bar having a pair of vertically opposite deep channels extending longitudinally in the top and'loottom faces v [thereof of such depth asV to leave onlyarela-` tively thin section therebetween, and having a vplurality ofY regularly spaced vertical grooves-.in

one side thereof, chopping said bar at right angles toits length into relatively-short lengths v each of which includes one of said vertical side grooves, breaking eachof said short lengths in different groups of uniformly shaped pieces one of the groups of Ypieces having one of said vertical grooves in one-side of each piece, and combining each piece of one group with one ofthe magnets with the verticalvgroovein onerfpieceY ofeach magnet providing a central hole therethrough.

. v MITCHELL P. CHRISTENYSEN. 

